Method of improving the properties of rubber and product



Patented June 6, 1933 UNITED STATES PATENT OFFICE WILLIS A. cannons, or lvrou'romnm, new JERSEY, assrenon TO THE NAUGATUGK CHEMICAL COMPANY, or NAU'GA'ruox, oommorronr, A ooaronn'rron or CON- NEGTICUT ETHOD or IMPROVING THE PROPERTIES or RUBBER Ann rnonuor {No m-awag. Original. application filed March a, 1930, Serial No. 434,462. Divided and. this application filed March a, 1930.

This invention relates to a method of improving the physical properties ofrubber and, to the product, more particularly to the improvement of the properties of alkaline rubbers, both in their unvulcanized and Vulcanized condition.

The present application is a division of my application Serial No. 434,462, filed March 8, 1930. Y In the preparation and manipulation of raw and reclaimed rubber for the manufacture of rubber or rubber and fabricarticles, certain physical properties are desired, such as ease of breakdown oftherubber on the mill, smooth calenderi-ng, and plasticity. In vulcanized articles, particularly those composed of rubber and fibrous .material which are subjected to a flexing action in use, such as tires, belting and hose, it is desired to obtain the greatest resistance to separation between the rubber and fibre caused by the flexing action. It has been found that raw rubbers which are decidedly alkaline, such as those to which alkaline materials have been directly added, and reclaimed rubbers which have been re claimed by the alkali process, "are deficient in some or all of the properties of easy breakdown, smooth calendering and extrud- 0 ing, and when such rubbers are incorporated in rubber and fabric articles, the articles are deficient in resistance to flexing.

The present invention therefore relates to a method for improving the physical properties of such alkaline rubber or alkaline reclaim during its manlpulation PIlOI to vulcanization and to improving the flexing ability of the vulcanized material when included in a rubber and fibre article.

invention is not limited" however in its application to such rubbers, but also decidedly improves the breakdown, calendering and extruding ability, and flexing ability of other rubbers such as all-solids-content-latex evap- Serial No. 434,463. 1

orated rubbers,- coagulated rubbers, and in general those which show antalkaline ash, and itis also applicable to combinations of any of the above rubbers.

i An object, of the present invention is to provide a-process for obtaining a vulcanized rubber of improved flexing characteristics. Another object is to provide a proc ess for softening, and in general improving the breakdown, calendering and extruding properties of rubbers during manufacturing operations. Another object is to provide improved rubber products, particularly vulcanized combinations of the treated material and fibers.

The invention consists broadly in incorporating in solid rubber having an alkaline ash, heavy metal water solublesalts of acids capable of decon'iposing alkali proteinates and alkali soaps, working to smooth, plastic condition, and if desired vulcanizing, and it also consists in the products obtained.

While as previously stated, the invention is applicable to raw rubber to which an alkali has been directly added or to an alkali treated reclaim, it is also of value in the treatment of any rubbers which show an alkaline ash, such as coagulated rubbers, allsolids-content-latex evaporated rubbers, or mixtures of any of these. In carrying out the invention the heavy metal salts, either as such or in solution, are incorporated with the solid rubber either on the ordinary form of mixingmill, or in a closed mixer or in any other suitable manner. Rubber to which such heavy metal salts have been added softens more readily in milling, is capable of smooth calendering and ex:

truding, and in general has its processing characteristics improved, and upon vulcanization displays a greatly increased flexing ability. As illustrations of the improvement lowing examples are given:

Ewample 5 Example 1 Spray dried rubber 100 100 Reclaim (alkaline)- 75 75 5 Spindle oil 5 5 70 Zinc oxide 5 5 P319 50 50 Heptaldehyde-aniline accelerator 5 .5 Smoked sheet 50 5 Zinc m -m 2 Reclaim (alkaline)- 75 75 sulphur 3. 3 75 Spindle oil 5 5 Zing nrirln 5 5 5 5 Heptaldehyde-aniline accelerator u Zinc nitrate 2 Cure g fg g g Sulphur 3. 75 3. 75 y 75 Cum Flexing in kilocyeles g g g $2 32 5 3 12. 8 22. O I 10' 5 27- 9 90 45# 4. 4 24. 4 10. 8 15. 4 80 13. 5 9. 7

Emample 6 Ewample 2 Smoked sheet rubber s3 s3 33 Blended roll brown (011 grade plantation rubber) 67 67 67 Tire reclaim (alkali process) 75 Tire reclaim (alkali process, with 1.6% ZnCl 75 Pale cr p 50 z oxide 5 5 Smoked sheet.- 50 50 Spindle 11 4 4 Whole W (alkali P 75 Heptaldehyde-aniline accelerator. 1. 1. 5 Whole tire reclaim (alkali process with 2% 21110 Sulphur 5 5 5 chloride) 75 gpindleg g g 1110 B Flexing in kilo- He taldeh de-aniline accelerator 0- 0i 7 Cure slll lhlll" y 3.75 3.75 cycles 90 24. 0 Cure 23. 9 21. 0 22. 8

95 unds 1693 2067 1735 Eammple 8 1659 100 In the above example the reclaim in the Spray dried rubber 100 100 Spindle oil 5 blank and the zinc chloride treated reclaim Zinc nirirle 5 I! Hepmdenydemflme accelerator were made ii 0111 the same batch 01 digested 40 lefiloride. 3. 75 blIe StOCk. 105

Ema/mplc '2 Flexing in Cure kllocycles Smoked sheet rubber 33 33 33 1I3 lendcdl roll lZIIfkVVIII (ofl grad)e plantation rubber). 67 67 (i7 ire rec aim a a i process 75 Tire reclaim (alkali process, with 1.4% ZnOI 45# Tire reclaim (alkali process, with 1% ZnCI 45# 5 1 Zinc 451? 9 1 Spindle oil 45# 7 3 Heptaldehyde-an ine accelerator.

Emample 4 50 *Spray dried rubber Whole tire reclaim (alkali process) 75 Whole tire reclaim (alkali process with 4.7% zinc chloride) Spindle oil 8 Zinc oxide 5 55 Heptaldehyde-aniline accelerator 0.5 Sulphur 5. 5

Flexi kiloc 33%; 2063 60 30' 45# 8.0 27. 6 1;;-

45 45# 6. 3 33. 0 e0; 4 6. 4 56.7 7 58. g i In the above example the reclaim 1n the blank and the zinc chloride treated reclaim a from latex containing formaldehyde and a sulphonated fatty Were made from mne basic tire tock 6 but not from the same digester run.

Ewample 8 Smoked sheet rubber 33 33 Blended roll brown (ofi grade plantation rubber) 67 67 Tire reclaim (alkali process) 75 Tire reclaim (alkali process, with 1.6% ZnClz) 75 Zinc oxide 5 Spindle oil 4' 4 Flexing in kllooycles l5. 5 34. (i 16. 1 36.2 16.4 30. 2 l4. 9 33. l

Tensile in pounds blank and the zinc chloride treated reclaim were made from the same. batch of digested tire stock.

The flexing data given in the above examples was obtained by the use of a commonly applied test in the tire industry, in which alternate plies of the rubber to be tested and fabric are built up to the desired thickness, cut into pads which are usually 5 x 8", and the pads then vulcanized in a mold. After vulcanization the pads are removed from themold and allowed to stand for about 36 hours, after which they are cut into strips usually 1" x 8". The strips are then subjected to a flexing test in which each strip is secured in a machine by its ends while the intermediate portion of the strip. is

in contact with a weighted pulley. The strip is then pulled back and forth around the pulley at the rate of about 160 cycles per minute until separation of the plies begins, and the number of cycles required to cause separation of the rubber from the fabric is noted.

In the above examples, the fabric plies were made according to the process disclosed in Hopkinson Patent No. 1,424,020, in which the fabric is weftless and consists only of parallel cords impregnated with and unit ed by rubber deposited directly from latex. The latex used for this purpose was compounded with spindle oil, formaldehyde-ethylamine condensation product, soap and sulphur.

Among other heavy metal water soluble salts which may be used in carrying out the process of the invention are mercuric chloride and zinc acetate. In general, it has been found that the heavy metal salts which are suitable for the process are water soluble salts of water soluble strong acids capable of decomposing alkali proteinates and alkali soaps, and having the ability to greatly di minish the alkalinity of the rubber, in some cases to a point approaching neutrality or somewhat below it, that is, to or below pH 7. The increase in flexing capacity of articles made according to the presentinvention is most pronounced where the rubberstreated are definitely alkaline, such as those to which fixed alkali has beenzadded,

and alkali processed reclaims,i. e. vulcanized rubbers which have been restored'to a plastic condition to render them suitable for re-use in rubber manufacturing operations, but there is also an improvement in the case of all rubbers showing analkaline ash, such as all-solids-content-latex rubbers, or with various combinations of any of the above rubbers.

The precise amounts of the heavy metal salt to be added will necessarily vary with the character of the mix, and, in general, the more alkaline the rubber mix, the greater the amount of any givenheavy metal Salt will berequired, and this amount can be readily determined by those skilled in the art. i

It Will be seen that by the use of the invention the flexing capacity of rubber and rubber. and fabric. articles may bevery greatly increased, and as a result either articles of marked superiority in this respect are obtained with the usual stocks, or much cheaper rubber stocks may be used and yet produce flexing capacity equalto or greaterthan much more expensive stocks at present in use. The invention is capable of wide use in the manufacture of all rubber articles Where good flexing is desirable, and it is of particular value for use with the usualvulcanized articles of commerce which are built up of layers of fabric and rubber, such as tires, belting, hose, etc. The improvement in milling propertiesis an other valuable feature of the invention, as

the softening of the rubber increases the speed of operation, and the uniform plasticity aids greatly in smooth and uniform calendering and extruding. Where the term rubber is used in the claims without qualification, it is intended to cover reclaim.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

.1. A method of improving the physical properties of rubber before and after its rio in a body of solid rubber by adding at the beginning of its breakdown a zinc salt 'of an acid selected from the group consistlng of hydrochloric and nitric acids, then incorporating the rubber in a rubber and fibre article, and vulcanizing.

3. A method of improving the physical properties of rubber before and after its vulcanization, which comprises incorporating in a body of solid rubber before vulcanization zinc chloride, working the rubber to a uniformly soft, plastic condition, incorporating it in a rubber and fibre article, and vulcanizing.

4. The plastic product of raw rubber and alkaline reclaim plasticized in the presence of a water soluble heavy metal salt of a water soluble acid strong enough to decompose alkali proteinates and alkali soaps, the pH of the water extract of said product not exceeding approximately 7.

5. The plastic product of an alkaline-ash solid rubber plasticized at the beginning of its breakdown by the addition of a zinc salt of an acid selected from the group consisting of nitric and hydrochloric acids.

6. A vulcanized article comprising fibre and a rubber stock derived from a mixture of solid rubber and a zinc salt of an acid selected from the group, consisting of nitric and hydrochloric acids.

7. A vulcanized article comprising laminations of fibrous material and a rubber stock derived from raw rubber, reclaim and a salt selected from the group consisting of zinc nitrate, zinc chloride, zinc acetate, and mercuric chloride.

8. A method of improving the physical properties of rubber before and after its vulcanization, which comprises incorporating inraw rubber and reclaim before vul canization, a water soluble zinc salt of a Water soluble acid capable of decomposing alkali proteinates and alkali soaps, forming a rubber and fibre article therefrom, and vulcanizing.

9. A method of improving the physical properties of rubber before and after its vulcanization, which comprises plasticizing raw rubber and reclaim by adding at the beginning of breakdown a salt selected from the group consisting of zinc nitrate, zinc chloride, zinc acetate and mercuric chloride, forming a rubber and fibre article from the product, and vulcanizing.

10. The process consisting of forming a rubber compound including raw rubber, reclaim and zinc chloride, making a rubber and fibre article therefrom, and vulcanizing, whereby the flexing properties of the article are increased.

Signed at Passaic, county of Passaic, State of New Jersey, this 5th'day of March, 1930.

WILLIS A. GIBBONS. 

